In conventional film cartridges, one end of photographic film is secured to a film spool, and the film is wrapped around the spool. In use, the cartridge is loaded into a photographic camera and the film is unrolled from the spool frame by frame and rolled onto a take-up spool, as is generally known in the art. During each frame advancement of the film, a high-energy lever in the camera is reset. The high energy lever is released by the shutter button and provides the energy for moving the camera shutter during exposure of the film.
When the last frame is exposed and the film is subsequently advanced, movement of the film will eventually be inhibited due to the securement of the end of the film to the spool. In automatic winding cameras, this condition typically will be sensed by a torque-limited drive mechanism, and the camera will be instructed either to stop winding the film or to go into rewind mode to rewind the film onto the cartridge spool. In manually operated cameras, the end of roll condition will be sensed by the user due to an increase in winding force.
One problem that may arise in the operation of a camera is that the high energy lever may become reset before or simultaneous with reaching the end of the film. In this situation, if the shutter button is pressed during rewind of the camera, the high energy lever will be released, and the film that is positioned behind the shutter will become exposed, thereby resulting in a double exposure.
In addition, due to a wide range of user strength and varying degrees of user knowledge regarding camera operation, sometimes the user will continue to wind the film after the end of film has been reached, resulting in the end of the film becoming detached from the spool. Such a condition is undesirable because the film typically is not salvageable without special processing.
Accordingly, it would be desirable to provide a mechanism, other than the attached interface between the film and the spool, for stopping film advance when the end of a roll of film has been reached. This mechanism would advantageously be activated before stress was placed on the interface between the film and the roll. In addition, when used in conjunction with metering perforations, such a mechanism should stop the film before the high energy lever of the camera is reset.